Increases in the frequency and severity of extreme rainfall might cause catastrophic submergence of underground spaces. Therefore, it is essential to predict the flood risk for proactive design. This study presents the methodology of acquiring risk level considering both flood intensity and evacuation difficulty. The flood momentum was computed by a 2D hydraulic flow model, and the flood intensity (FI) was employed to evaluate the consequence of flooding. To investigate the level of evacuation difficulty, the spatial layout of rooms, together with walking speed, were considered in the risk analysis process. If stormwater runoff enters an underground space, zones far away from the inlet usually have low risk levels. However, when the level of evacuation difficulty was considered, the risk level was dependent on the evacuation distance and location of the inlet and exit. If people are in zones with a risk level of 4 or 5, a rapid evacuation is necessary for preventing human casualties. The proposed methodology incorporated with the inundation model can be applied to any underground space regardless of the location of stairs, the number of exits, shape of rooms, or layout of the floor. Consequently, it will contribute to mitigating flood damage in an underground space.

The optimal size of a diversion structure should be carefully studied to ensure economic viability and safety during construction. In practice, to determine the size of a diversion structure, design flood frequency is selected as the suggested return period presented by the design standard, which is presented differently. This study proposes a methodology for the design of a diversion structure with a concrete cofferdam adopting risk analysis to reflect the more practical hazard and risk of diversion structure during dam construction. The proposed methodology is based on a risk-based least-cost design process and risk analysis. The optimization result is presented as the lowest expected monetary value, which accounts for construction cost, reconstruction cost, and delay liquidated damage with the failure probability and recovery cost with the overflow probability. This methodology was applied to the case study of the Gulpur hydropower project in Pakistan. The results showed that the optimal design flood frequency is 1 year for a recovery cost of USD 0.5 mil. and 1~2 years for a recovery cost of USD 1.0~2.0 mil. with 3, 4, and 5 years of the usage period of the diversion structure. Furthermore, 2~10 years is the optimal value for a recovery cost of USD 3.0~4.0 mil. These results indicated that the optimal design flood frequency increases as the recovery cost and usage period of the diversion structure increase. The results of the study reveal that the recovery cost and the period of use of the diversion structure affect the design flood frequency of the diversion structure. From a design perspective, the period of use is determined by the construction period of the project or the construction method, whereas the recovery cost depends on the countermeasure method. Therefore, after preparing a proactive plan and estimating the recovery cost, the design flood frequency for the diversion structure should be determined.

Helicopters that can respond rapidly to medical accidents are used frequently on sites that require firefighting and medical services. Therefore, Korea recommends that high-rise buildings install heliports for easy evacuation through an alteration to the Building Act. However, because heliport installation laws are inconsistent with the specifications of each heliport on high-rise buildings being different, helicopter landing in emergencies may be hindered. This may result in failure to respond to an accident. To minimize complications, the International Civil Aviation Organization (ICAO) and the Federal Aviation Administration (FAA) determine helicopter take-off and landing regulations as well as heliport operations. This method minimizes human error in pilots and allows for the maintenance of facilities, minimizing technical errors. Therefore, this study investigates the current status of domestic rooftop heliports and attempts to derive measures that improve domestic legislation through comparison with overseas standards to identify higher standards.

Gas pipelines are buried and installed across rivers to supply the gas necessary for daily life. When crossing rivers, gas pipelines are typically installed on bridges; however, when installation on bridges is not feasible, the pipelines are buried in riverbeds. This study utilized both a one-dimensional model (HEC-RAS) and two-dimensional models (SMS) to simulate river flow and estimate the potential for scour and deposition around buried pipelines. The hydrodynamic simulations considered critical factors, including sediment transport, river discharge, and geological characteristics, to derive the maximum scour depth and assess the risk of pipeline exposure. The findings from the long-term and short-term simulations confirmed that riverbed changes due to natural hydrological events do not exceed the minimum burial depth standards, thereby ensuring pipeline safety. In addition, the study proposed specific reinforcement measures tailored to local site conditions, addressing concerns of continuous subsidence and ensuring long-term structural stability. This research offers important insights into pipeline risk management and contributes to the development of more effective regulatory standards for gas pipelines buried in riverbeds, enhancing both their safety and environmental sustainability

Climate change has exacerbated flood risks for urban infrastructure, rendering sewage treatment facilities (STFs) particularly vulnerable due to their typical low-lying topographic placement. However, conventional flood risk assessment methodologies often rely solely on physical hazard parameters such as inundation depth, neglecting the functional interdependencies and operational criticality of individual treatment units. To address this limitation, this study proposes the Integrated Hydro-Operational Risk Assessment (IHORA) framework. The IHORA framework synthesizes 2D hydrodynamic modeling with a modified Hazard and Operability Study(HAZOP) study to systematically identify unit-specific physical failure thresholds and employs the Analytic Hierarchy Process (AHP) to quantify the relative operational importance of each process based on expert elicitation. The framework was applied to an underground STF under both fluvial flooding and internal structural breach scenarios. The results revealed a significant risk misalignment in traditional assessments; vital assets like electrical facilities were identified as high-risk hotspots despite moderate physical exposure, due to their high operational weight. Furthermore, Cause–Consequence Analysis (CCA) was utilized to trace cascading failure modes, bridging the gap between static risk metrics and dynamic emergency response protocols. This study demonstrates that the IHORA framework provides a robust scientific basis for prioritizing mitigation resources and enhancing the operational resilience of environmental facilities.

Flood safety in subway stations depends not only on when floodwater reaches critical locations but also on whether evacuation routes remain usable long enough for evacuation to be completed. Conventional hydraulic outputs do not directly integrate these location- and route-based requirements. This study develops a response-time-based framework linking location-specific Available Safe Egress Time (ASET), hydraulic route-hazard screening, inundation-induced walking delay, and Required Safe Egress Time (RSET). Unlike depth- or ASET-only assessments, the framework evaluates evacuation-time feasibility and route walkability separately and interprets them jointly. It was tested through 36 simulations of a subway-station concourse varying entrance and elevator inflows and internal-door connectivity, with warning delay, evacuation demand, and exit capacity considered in RSET. Where the thresholds were reached, the office near the entrance inflows had an approximately 81% shorter wet-cell onset time and a 59% shorter ASET at 0.30 m than the more distant sump and drainage pump room. Higher and multiple inflows accelerated flood arrival, whereas door connectivity mainly affected subsequent water redistribution. In contrast, pump-room routes more frequently exceeded hydraulic walkability thresholds, and flooding increased travel time on the longest route to nearly four times its dry value. Baseline RSET more than doubled when the assumed evacuation demand increased tenfold to an upper-bound value that does not represent station occupancy. These findings distinguish time-critical from route-critical locations and show that a positive ASET–RSET balance does not ensure route walkability. The framework provides an operationally interpretable link between time-dependent hydraulic outputs and subway-station response planning.